Energy and Civilization A History By Vaclav Smil

2: Energy in Prehistory

Human walking costs about 75% less energy than both quadrupedal and bipedal walking in chimpanzees.

The brain’s specific energy need is roughly 16 times that of skeletal muscles, and the human brain claims 20–25% of resting metabolic energy, compared to 8–10% in other primates and just 3–5% in other mammals

Fish and Lockwood (2003), Leonard, Snodgrass, and Robertson (2007), and Hublin and Richards (2009) confirmed that diet quality and brain mass have a significantly positive correlation in primates, and better hominin diets, including meat, supported larger brains, whose high energy need was partly offset by a reduced gastrointestinal tract

While extant nonhuman primates have more than 45% of their gut mass in the colon and only 14–29% in the small intestine, in humans those shares are reversed, with more than 56% in the small intestine and only 17–25% in the colon, a clear indication of adaptation to high-quality, energy-dense foods (meat, nuts) that can be digested in the small intestine.

Increased meat consumption also helps to explain human gains in body mass and height, as well as smaller jaws and teeth.

Whereas allometric equations predict about five 50 kg mammals/km2, chimpanzee densities are between 1.3 and 2.4 animals/km2, and the densities of hunter-gatherers surviving into the twentieth century were well below one person/km2 in warm climates, only 0.24 in the Old World and 0.4 in the New World

Mollusk collecting, fishing, and near-shore hunting of sea mammals sustained the highest foraging densities and led to semipermanent, even permanent, settlements. The coastal villages of the Pacific Northwest, with their large houses and organized communal hunting of sea mammals, were exceptional in their sedentism.

Generally less than 30% of the ingested phytomass is digested; most of it is respired, and in mammals and birds only 1–2% of it is converted into zoomass. As a result, the most commonly hunted herbivores embodied less than 1% of the energy initially stored in the phytomass of the ecosystems they inhabited. This reality explains why hunters preferred to kill animals that combined a relatively large adult body mass with high productivity and high territorial density: wild pigs (90 kg) and deer and antelopes (mostly 25–500 kg) were common targets.

In light of the unimpressive physical endowment of early humans and the absence of effective weapons, it is most likely that our ancestors were initially much better scavengers than hunters

Large predators—lions, leopards, saber-toothed cats—often left behind partially eaten herbivore carcasses. This meat, or at least the nutritious bone marrow, could be reached by alert early humans before it was devoured by vultures, hyenas, and other scavengers.

human bipedalism and ability to sweat better than any other mammal made it also possible to chase to exhaustion even the fastest herbivores

Horses lose water at an hourly rate of 100 g/m2 of their skin, and camels lose up to 250 g/m2, but people lose more than 500 g/m2, with peak rates of more than 2 kg/hour

People can also drink less than they perspire, and make up for any temporary partial dehydration hours later. Running turned humans into diurnal, high-temperature predators that could chase animals to exhaustion

Hunters running barefoot reduced their energy costs by about 4% (and had fewer acute ankle and chronic lower leg injuries) than modern runners with athletic shoes.

Late Pleistocene hunters may have become so skillful that many students of the Quaternary era concluded that hunting was largely (even completely) responsible for a relatively rapid disappearance of the late Paleolithic megafauna, animals with a body mass greater than 50 kg

All wild meat is an excellent source of protein, but most of it contains very little fat, and hence it has very low energy density—less than half that of grains for small, lean mammals. Not surprisingly, there was a widespread hunting preference for large and relatively fatty species.

Thanks to its high fat content (about 15%), salmon has an energy density (9.1 MJ/kg) nearly three times that of cod.

The high energy density of blubber (about 36 MJ/kg) and muktuk (skin and blubber, which also has a vitamin C content comparable to that of grapefruit) resulted in a more than 2,000-fold energy gain in hunting.

A food supply dependent on a few seasonal energy flows required extensive, and often elaborate, storage. Storage practices included caching in permafrost; drying and smoking of seafood, berries, and meats; storing of seeds and roots; preservation in oil; and the making of sausages, nut-meal cakes, and flours. Large-scale, long-term food storage changed foragers’ attitudes toward time, work, and nature and helped stabilize populations at higher densities

contrary to all popular claims about the benefits of Paleolithic diets, we still cannot reconstruct the representative composition of pre-agricultural subsistence.